Schematic cartoon of the deep water cycle

This image is a schematic cartoon of the deep water cycle. Water percolates through the oceanic tectonic plates at the surface, hydrating the oceanic crust and lithospheric mantle below it. When the oceanic plates subduct, part of the water is released at shallow depths (<250 km) into the mantle wedge above the slab. This triggers mantle melting and the formation of volcanic arcs at the surface, in the overriding plate. The rest of the water stays in the slab and is carried deep down into the mantle. Depending on the subduction dynamics, this water can either be released at the mantle transition zone (410-660 km), where large amount of water can be stored in nominally anhydrous minerals, or go even deeper, up to the core-mantle boundary. Part of the water present in the mantle can then be released at the surface again by melt at intraplate volcanoes and mid-ocean ridges as it is transported by plumes and mantle convection.